DOES DIETARY DIPEPTIDE CONFIGURATION MATTER IN FISH NUTRITION?

Dietary amino acids (AA), critical for tissue protein synthesis, can be provided in different molecular forms: protein-bound, free amino acids (FAA), or peptides .  Fish express several AA transporters in the digestive tract but only two peptide transporters, Pept-1 and Pept-2 , have been identified. Although Pept-1 is able to facilitate transport of 400 di- and 8,000 tripeptides across the membrane not all AA configurations in these peptides  have been reported to elicit transport currents in biological membranes. The objective of this study was to examine the effect of a wheat-gluten-based diet  supplemented with  lysine in  different molecular forms on growth, PepT1  mRNA transcript levels , and whole body FAA composition in  zebrafish Danio rerio.

Fish of an initial size  of ~0.03 g were randomly distributed into 12 glass aquaria , 30 fish per aquarium. Fish were fed four wheat-gluten based diets supplemented with  one of the following: lysine- glycine  dipeptide (Lys-Gly ), glycine-lysine dipeptide (Gly-Lys) , free lysine (Free Lys),  or no lysine (-Lys).  After 30 days the mean weight  and weight gain  of the fish fed  with  the (-)Lys diet was smalle r  compared to the other three groups . No differences were found, however, between Lys-Gly, Free Lys , and Gly-Lys groups .  The Pept1 gene expression in zebrafish intestinal tract showed  that  Lys-Gly induced higher expression compared to Free Lys and (-)Lys groups but no difference was detected between Lys-Gly and Gly-Lys groups. The Pept1 expression was also not different between Gly-Lys, Free Lys, and (-)Lys groups (Figure 1).

The study showed that zebrafish is able to utilize different forms of dietary Lys efficiently for growt h and  both Lys-Gly and Gly-Lys  seem to have a similar effect on intestinal Pept1 gene expression contradicting previous studies  that reported  lower affinity of Pept1 towards Gly-Lys. Whole-body FAA composition will be presented during the oral presentation.